An internal combustion engine mounted on a vehicle or the like is provided with cooling water in order to cool the internal combustion engine that generates heat. The cooling water is supplied to the internal combustion engine by a water pump and absorbs heat of the internal combustion engine. The cooling water which has absorbed the heat is supplied to a radiator and releases the heat of the cooling water by the radiator, and flows into the water pump again. In other words, the cooling water circulates between the internal combustion engine and the radiator by the water pump, and releases the heat of the internal combustion engine at the radiator.
In a cooling apparatus of the internal combustion engine described in Patent Document 1 (corresponding to the internal combustion engine cooling system in the present application), the cooling water discharged from a cooling water pump (corresponding to the water pump in the present application) is branched into two, with one being supplied to a cylinder block of the internal combustion engine, and the other being supplied to a cylinder head. Then, the cooling water flowed out from the cylinder block and the cylinder head merges after passing a thermostatic valve for the cylinder block and a thermostatic valve for the cylinder head, respectively.